A paper-like material, for example, can be obtained by a method of papermaking a dispersion essentially including fibers and a resin binder (papermaking method). As a resin binder used in the papermaking method, a water-soluble resol-type phenol resin, a phenol resin emulsion, a novolak type phenol resin powder cured with hexamethylenetetramine, or a resol type phenol resin powder is used.
However, the papermaking method has the following problems.
(1) In the case of using a water-soluble resol-type phenol resin or a phenol resin emulsion as a resin binder, aggregation is generally performed with a fixing agent such as aluminum sulfate or polyaluminum chloride. At this time, efficiency of the aggregation is not good, and thus, the resin binder may flow out into wastewater at the time of the papermaking (environmental load is high).
(2) In the case of using a novolak type phenol resin as a resin binder, a mixture obtained by simply mixing a novolak resin and a curing agent such as hexamethylenetetramine is used. However, since these are simply mixed with each other, the curing agent such as hexamethylenetetramine may be dissolved in water and easily washed away, and thus, environmental load may increase at the time of the papermaking like the above case. In addition, since the curing agent is washed away, strength of a cured product obtained by heat curing after the papermaking may not be sufficient.
(3) In the case of using a resol resin as a resin binder, the resol resin normally includes approximately 0.05% to 0.3% of free formaldehyde and approximately 5% to 10% of free phenol. Accordingly, free monomers thereof are easily washed away together with water at the time of the papermaking, and thus, environmental load may increase like the above cases. The environmental load can be decreased by using a resol resin in which the amount of free monomers in the resol resin is decreased, but flowability of the resin is poor, and as a result, strength of a cured product obtained by heat curing after the papermaking may not be sufficient.
In order to solve these problems, for example, a technology of using a resin composition including a phenol-based resin powder and an epoxy resin powder as a resin binder has been disclosed (for example, see PTL 1). However, even in the case of using a dispersion including the resin composition disclosed in PTL 1, it is insufficient to decrease the environmental load. In addition, the resin composition was insufficient to function as a binder which binds fibers, and as a result, heat resistance and strength of a product (sheet product) to be obtained are insufficient.